Grassland Phosphorus and Nitrogen Fertiliser Replacement value of Dairy Processing Dewatered Sludge

Abstract Dairy processing sludge is currently a bio-based fertiliser being spread to grassland without knowledge pertaining its phosphorus (P) or nitrogen (N) replacement value. This creates uncertainty of desired crop yield achievement and unproductive nutrient recycling also poses great challenge the dairy milk industry in promoting their food by-product as valuable recyclable fertiliser. Therefore four representative samples, i.e. two activated (aluminium-precipitated (Al-sludge) iron-precipitated (Fe-sludge)), lime-stabilised calcium-precipitated (Ca1- Ca2-sludge), were examined at field scale assess P N availability for uptake comparison reference mineral fertilisers over one seasonal year. The plots set-up on light textured clay loam soil within optimum plant available (Morgan's index 3, medium / adequate level) separate adjoining areas consisting experiments. Each experiment consisted 40 (each 8×2 m2) 10 treatments with 4 replications arranged randomised complete block design. All (40 kg-P ha−1) (rates 0–50 produced similar yields uptake, was not affected by applications despite presence high Al, Ca Fe. During there no significant change (stayed 3) indicating that treatment caused decline into 2 (i.e. low level), therefore replacing removed crop. only Morgan's observed Ca-sludge treatments, but this due reagent overestimating conditions. From trial significantly higher grass Fe both Ca-type applied than control (zero N) plot during 1st harvest, while statistical difference subsequent harvests (up 4th harvesting). value (derived from response) samples be order (54%)>Ca2 (25%)>Ca1 (22%)>Al (8%) greater promise efficiency types. Overall these sludges show application longer term trials other types considering environmental aspects (losses soil, water air) can further optimize management an alternative chemical